The global problem addressed by this proposal is how does the central nervous system (CNS) control a structure as complex as the primate hand? To begin to address this question, four Specific Aims are proposed that address three outstanding issues in the neural control of reach-to-grasp. The studies will use chronic single unit recordings in the primary motor cortex (M1) of monkeys trained to perform various reach-to-grasp movements. Extensive monitoring of arm and hand kinematics, grasp forces and the activity of arm and extrinsic/intrinsic muscles of the hand will be done. Statistical and analytical tools including regression analyses and data reduction techniques will be used to extract the neural representation of hand shape/object shape, kinematics, grasp forces and EMG activity. First, findings from psychophysical, lesion, and electrophysiological studies suggest that the CNS, at least in part, reduces the number of degrees of freedom by controlling the hand as a unit. Specific Aims 1 and 2 will address the hypothesis that neurons in the hand area of M1 encode and control hand shape/object properties, reflecting this global control of the hand. Second, early investigations into hand movements categorized prehension into two broad classes, power and precision grip and more elaborate classification systems followed. A prediction of these categorical schemes is that the CNS explicitly controls grasp type. More recent psychophysical studies, however, suggest that a strict division of hand posture into power and precision grasps does not occur. Specific Aim 3 will test the alternative hypothesis that power and precision are part of a continuum of hand postures in which hand shape is primarily controlled. A third major contemporary hypothesis is that reach and grasp are controlled by two independent but coupled channels: a "transport" channel that extracts information about the spatial location of objects to guide the reach and a "manipulation" channel that extracts information about the intrinsic properties of the object such as size and shape to guide hand shape. Although psychophysical results suggest that the two components are coupled, there is virtually no single unit data addressing this question. In Specific Aim 4 the hypothesis is tested that the reach and grasp components are coupled at the neuronal level in M1. In general understanding how the CNS controls prehension is a critical step in understanding human movements. In the future understanding the signals controlling grasp could prove useful for controlling prosthetic devices in patients with brain injury.